Legend of Heroes

legendOfHeroes.dart

import 'package:flutter/material.dart';

/// The class controls every [Hero] widget has it's own name.
/// If the code generates [Hero.tag] by some model derived algorithm,
/// especially in list widgets such as [ListView.builder], the tag may
/// conflict in some case. The class has internal tag list and if same tag
/// is used twice, it does not insert [Hero] in that case.
/// ```dart
/// Widget build(BuildContext context) {
///   final heroInserter = HeroInserter();
///   return ....
///      heroInserter.hero(
///        tag: 'aaaa',
///        child: const Text('aaaa')
///      )
///    ...
/// }
/// ```
class HeroInserter {
  final _names = Set<String>();

  /// Insert [Hero] widget if same [tag] is never used.
  Widget hero({String tag, Widget child}) {
    if (!_names.add(tag))
      return child;
    return Hero(tag: tag, child: child);
  }

  void clear() => _names.clear();
}

/// The class prevents [Hero] tag duplications on [Widget] tree if you use
/// `LegendOfHeroes.of(context).hero` to insert [Hero] widgets.
/// ```dart
/// Widget build(BuildContext context) {
///   return LegendOfHeroes(
///     child: ...
///       ...
///           LegendOfHeroes.of(context).hero(
///             tag: 'some_name',
///             child: ...
///           )
///   );
/// }
/// ```
class LegendOfHeroes extends StatefulWidget {
  final Widget child;

  LegendOfHeroes({@required this.child});

  @override
  _LegendOfHeroesState createState() => _LegendOfHeroesState();

  /// Obtain [HeroInserter] held by the ancestor [LegendOfHeroes] widget.
  static HeroInserter of(BuildContext context) {
    final state = context.ancestorStateOfType(const TypeMatcher<_LegendOfHeroesState>());
    if (state is _LegendOfHeroesState) {
      return state.inserter;
    }
    throw Exception('LegendOfHeroes is not found in the widget tree.');
  }
}

class _LegendOfHeroesState extends State<LegendOfHeroes> {
  final inserter = HeroInserter();
  @override
  Widget build(BuildContext context) {
    inserter.clear();
    return widget.child;
  }
}